section {
  width: 400px;
  height: 400px;
  border: solid 1px black;
  position: absolute;
  left: 50%;
  top: 50%;
  margin-left: -200px;
  margin-top: -200px;
}
section div {
  width: 100px;
  height: 100px;
  position: absolute;
  background-color: #ddd;
  border: solid 1px black;
}
section div:first-child {
  left: 50%;
  top: 50%;
  margin-left: -100px;
  margin-top: -100px;
}
section div:nth-child(2) {
  left: 50%;
  top: 50%;
  margin-top: -100px;
}
section div:nth-child(3) {
  left: 50%;
  top: 50%;
  margin-left: -100px;
}
section div:last-child {
  left: 50%;
  top: 50%;
}
